I write about a lot of depressing subjects, and sometimes a change of pace is welcome. Mary Roach, billed as “America’s funniest science writer,” has followed up on her earlier explorations of cadavers (Stiff), sex (Bonk), the afterlife (Spook), and survival on spaceships (Packing for Mars) with a new book entitled Gulp: Adventures on the Alimentary Canal.

Forget all that mythology about diet, detoxification, and 10-year-old hamburger accretions in the bowel. The reality of human digestive physiology is far more interesting and has the extra-added attraction of being true. And in Roach’s hands, often howlingly funny. She is a hands-on investigative reporter who is ready to try anything; among other adventures she inserts her entire arm in a cow’s stomach. Her highly entertaining odyssey takes her to Igloolik to eat narwhal skin, to a dog food tasting lab in Missouri, to Minnesota to observe a fecal transplant, and to strange and exotic outposts at the cutting edge of science, populated by colorful characters.

She also delves into intriguing vignettes of history. Did you know that when President Garfield was dying from complications from an assassin’s bullet, he was fed exclusively by rectum? She gives the recipe and describes the offensive odors that pervaded the whole house.

She describes how the Catholic Church grappled with the question of whether rectal consumption of beef broth would break one’s Lenten fast. Pharmacists had been selling bouillon enemas to nuns and other pious Catholics to sustain them through the fast. According to the Vatican rules on fasting, food was defined as passing through the mouth, so nourishment by enema was apparently okay. But they weren’t entirely sure, and they actually considered applying the scientific method to matters of faith:

An experiment was proposed whereby volunteers would be fed strictly by rectum. If they survived, the enema would have to be considered food and therefore banned. If they didn’t, the definition would remain as is, and some vigorous penance would be in order. In the end, nobody volunteered and the nuns continued…to welcome the clysters.

Roach tells us that hydrogen sulfide, the odor of rotten eggs, is as lethal, molecule for molecule, as cyanide. It is offensive to our noses at 10 parts per million, but above 150ppm we can no longer smell it: it paralyzes the olfactory nerves. It can reach 1000ppm in manure pits, enough to cause respiratory paralysis and suffocation. Without the odor to warn them, people collapse and die, as do those who try to rescue them. In one case, a farmer went into a manure pit to unclog a pipe. When he collapsed, a worker tried to rescue him, the farmer’s mother hurried down the ladder to help both of them, and her son died trying to help her: a chain of death involving 4 people. And a team of pathologists working in a poorly ventilated autopsy room were nearly overcome by fumes from the victims’ bodies.

We learn about the virtues of spit, how to survive being swallowed alive, why some animals would die if they didn’t eat their own feces, how competitive eaters train, the mechanics of transporting contraband in swallowed packets or by rectal insertion, flatulence research (one curious finding: men fart more, but women’s farts smell worse), why the stomach doesn’t digest itself (actually, it does, but the stomach lining constantly renews itself), why increasing fiber in the diet might be bad for you, the role of chronic constipation and megacolon in Elvis’ death, and how surgeons attempted to cure diarrhea by excising a section of bowel and re-installing it backwards to achieve reverse peristalsis (this didn’t work).

If you read this book, you will be amused and will learn many things, although some of them might not make for suitable dinner conversation.